System And Method For Color Measurement With Compensation For Second-Order Diffraction Error

The present invention is directed to an apparatus, as well as systems and methods for measuring the color properties of a sample or item and evaluating the measurements to compensate for second-order diffraction errors present in the measurement data.

For a grating-based spectrophotometer, such as Datacolor's DC1000, due to second-order diffraction effect (SODE), the grating will deliver part of a certain wavelength (such as 350 nm) light towards the same direction of the light that has twice the wavelength (such as 700 nm). Therefore, if not compensated, when the light sent into the gratings has UV content in the range of 340 nm˜380 nm, the measured signal in the range of 680 nm˜760 nm will be distorted. This distortion is referred to as a second-order diffraction effect.

Traditionally, linear-variable long-pass filters are used to remove this second-order diffraction effect in practice and are manufactured into tens of thousands of spectrometers each year. However, these types of filters are expensive to produce and they require careful alignment to the detector during the spectrometer's manufacture.

Alternatively, as taught in patent granted to Xu et. al. (U.S. Pat. No. 9,188,486B1) (herein incorporated by reference in its entirety) a method was developed to compensate second-order diffraction error without using such a filter. However, the Method described by Xu et. al still requires certain production process changes during manufacturing.

Therefore, what is needed in the art is an analytical and methodological approach that allows for the correction of second-order diffraction effects in measurements without the need to add costly equipment or detailed maintenance routines. Furthermore, what is needed in the art are systems and methods that provide accurate color and light measurements while also compensate for second-order diffraction error in a low cost and easy to implement manner.

In one or more implementations, an apparatus, system or method is provided to compensate for second-order diffraction error (SODE) in connection with color or light measurements of a sample. In one particular implementation, methods and systems have been developed to compensate for SODE in a spectrophotometer by using a set of wavelength dependent compensation factors or diffraction ratios. The compensation factors can be generated with a narrow-band light source that covers the lower part of the wavelength range of the spectrophotometer but not the higher part of the wavelength range where the second-order diffraction error occurs and can be applied to the raw data of the spectrophotometer to compensate for the second-order diffraction error. Alternatively, the compensation factors can be generated based on some empirical data, or some mathematical model, or training with both UV included and UV excluded data of one or more samples.

In a further arrangement, an apparatus for measuring the characteristics of a sample is provided, the apparatus comprising: a narrow-band light source; a spectrophotometer having at least a light measurement sensor and a processor, the light measurement sensor configured to measure the wavelengths of light within the narrow-band of the narrow-band light source to obtain a base signal at a first wavelength range, and a second-order signal at a second wavelength range, wherein the second wavelength range is greater than the first wavelength range and has no overlap with the first wavelength range; the processor configured to calculate a diffraction ratio value corresponding to a relationship of the second-order signal to the base signal; obtain a measurement of the sample using the spectrophotometer; and calculate corrected measurement value using at least the diffraction ratio value and the measurement signal value.

By way of overview and introduction, various embodiments of the apparatus, systems and methods described herein are directed to the compensation of second-order diffraction errors (SODE) in spectrophotometer measurements. In particular, the various embodiments of the systems, methods and apparatus described herein are directed to the correction of errors encountered in spectrophotometer measurements through the use a set of wavelength dependent compensation factors, herein referred to as diffraction ratios.

As shown,illustrates the elements of one embodiment of a system or device for obtaining measurements of a sample that have been compensated for second-order diffraction error. In one arrangement such a system, device or apparatus includes a processor, at least a narrow-band light source, at least a broadband light source, a light measurement sensor, a database or data storage device, and a remote computer or display device.

In one or more particular implementations, the light sourcesandare integrated into the same instrument. In this configuration, light generated by light sourceshines light onto the sample. This configuration is similar to how the light sourceis configured to illuminate the sample. Alternatively, a single light source (not shown) can be configured to produce both the narrow-band light and the broadband light. For example, the output of an illuminant can be tuned or set to a desired range. Under such a configuration, the diffraction ratio can be obtained using light sourceor, so long as the light source has been tuned or tailored to produce narrow-band light. Sample measurements are obtained using light source, and these measurements are then compensated using diffraction ratio generated using the light source.

In an alternative configuration, the light sourceis configured to direct light from the light sourcedirectly onto the light measurement sensor. In this configuration, the positioning of the light sourceor its location in the instrument is separate and distinct from the location and position of light source. In this configuration, diffraction ratio values can be obtained using light. Here, sample measurements are still obtained using light, and can be compensated using diffraction ratio obtained using the light source.

In yet a further implementation, the light sourceis not co-located in the measurement instrument. Here, only light sourceis part of the instrument. A separate narrow-band light sourceis used to generate the diffraction ratio. For example, an external light sourceis used to direct light to the measurement sensorto obtain the diffraction ratio. Once the diffraction ratio is obtained, sample measurements of a samplecan be obtained through the use of the diffraction ratio.

In one or more arrangements, the measurement device such as a spectrophotometer, is configured to measure a measurement target. In one particular implementation, the measurement target is a reflective or transmissive sample, such as a tile. In this configuration, the measurement device is configured to illuminate the sample and obtain a measurement. However, in some instances, the measurement target is an article that emits its own light. For example, where the measurement target is a lamp or display device, then the light from the light sourceis not needed to obtain measurements. Here, the color measurement instrument is configured to measure the color of a light source such as a computer monitor or other display devices. In this implementation, the narrow band light source is still used to obtain the diffraction ratio, however there is no need to use the light sourceto illuminate the measurement target.

It will be appreciated that in one or more arrangements, the elements presented incan be incorporated into a single form factor, such as a commercial grade spectrophotometer. In another particular implementation, the elements described herein are separate or partially separate components that communicate with one another through wired or wireless connections.

With continued reference to, one or more illuminator(s)is configured to emit light and cause such emitted light to either directly or indirectly illuminate the light measurement sensor. In one instance, the illuminatoris a single lighting element. However, in alternative implementations, the illuminatoris a collection of separate lighting devices that are configurable to produce a light with certain wavelength bands. For instance, the illuminatorcan, in one implementation, be one or more discrete light emitting elements, such as LEDs or OLEDs; fluorescent, halogen, xenon, neon, fluorescent, mercury, metal halide, HPS, or incandescent lamps; or other commonly known or understood lighting sources.

In one arrangement, the illuminatoris one or more narrow-band LEDs. In one particular implementation, the illuminatoris a UV LED. In another arrangement, the illuminatoris a broadband light source configured with one or more UV band-pass filters positioned between the illuminatorand the measurement sensor.

With continued reference to, one or more illuminator(s)is configured to emit light and cause such emitted light to either directly or indirectly illuminate the light measurement sensor. For instance, the illuminatoris configured to direct light towards a sample, which is then transmitted or reflected to the light measurement sensor.

In one instance, the illuminatoris a single lighting element. However, in alternative implementations, the illuminatoris a collection of separate lighting devices that are configurable to produce a light with certain wavelength bands. For instance, the illuminatorcan, in one implementation, be one or more discrete light emitting elements, such as LEDs or OLEDs; fluorescent, halogen, xenon, neon, fluorescent, mercury, metal halide, HPS, or incandescent lamp; or other commonly known or understood lighting sources. In one arrangement, the illuminatoris one or more wide-band LEDs. In one or more implementations, the illuminatoris a light source incorporated into a spectrophotometer, such as Datacolor's DC1000.

In one or more implementations, the illuminatoror illuminatorincludes a lens, filter, screen, enclosure, or other elements (not shown) that are utilized in combination with the light source of the illuminatoror illuminatorto direct a beam of illumination, at a given wavelength, to the light measurement sensor.

In a particular implementation, the illuminatoris operable or configurable by an internal processor or other control circuit. Alternatively, the illuminatoris operable or configurable by a remote processor or control device having one or more linkages or connections to the illuminator. As shown in, illuminatoris directly connected to a processor or computer.

Continuing with, light generated by the illuminatoris captured or measured by one or more measurement devices, such as the light measurement sensor. In one or more implementations, the illuminator or light sourceis configured to send or shine light onto the wall of an integrating sphere (not shown). For example, where the measurement device includes an integrating sphere, the illuminator or light sourceis configured to send light towards the inner surface of the integrating sphere. From there, light is then directed to the light measurement sensor. For example, where the measurement device is the DC1000, the integrating sphere is the integrating sphere found therein. In one or more particular implementations, where the illuminatoris not incorporated within the measurement device, the measurement device includes a door, window, trap, or other arrangement that allows light from an external illuminator to reach the light measurement device.

Here, the light measurement sensorcan be a color sensor or image capture device. For example, the light measurement sensoris a scientific CMOS (Complementary Metal Oxide Semiconductor), CCD (charge coupled device), colorimeter, spectrometer, spectrophotometer, photodiode array, or other light sensing device and any associated hardware, firmware and software necessary for the operation thereof. In one particular implementation, the light measurement sensoris a multi-channel spectral sensor or similar device. In one or more implementations, the light measurement sensor(s)described herein, has multiple optical, NIR or other wavelength channels to evaluate a given wavelength range. However, other potential sensor configurations and wavelength channels having varying numbers of sensor channels and operational characteristics are understood and appreciated.

In a particular implementation, light measurement sensoris the same sensor present in Datacolor's DC1000 spectrophotometer (the technical specifications of which are herein incorporated by reference in its entirety).

In a further arrangement, the light measurement sensoris configured with diffraction grating and other optical components. For example, in one or more implementations, the light measurement sensorincludes high-pass filters.

In one or more configurations, the light measurement sensoris configured to generate an output signal upon light striking a light sensing portion thereof. By way of non-limiting example, the light measurement sensoris configured to output signals in response to light that has been directly or indirectly emitted by the illuminator (eitheror).

For instance, light measurement sensoris configured to generate a digital or analog signal that corresponds to the wavelength or wavelengths of light that are captured or received by the light measurement sensor. In one or more configurations, the light measurement sensoris configured to output spectral information, RGB information, or another form of multi-wavelength data representative of light reflected off a sample.

As shown inthe light measurement sensor, or spectral sensor, is configured to transmit one or more measurements to a processing platform, such as processor. In one or more configurations, at least one light measurement sensoris directly connected to processor. However, in one or more implementations, one or more light measurement sensors(where there are multiple such sensors) are equipped or configured with network interfaces or protocols usable to communicate over a network, such as the internet. In this configuration, measurements made by light measurement sensorsare sent to a remote processor for evaluation and analysis.

Alternatively, at least one light measurement sensoris connected to one or more computers or processors, such as processor, using standard interfaces such as USB, FIREWIRE, Wi-Fi, Bluetooth, and other wired or wireless communication technologies suitable for the transmission measurement data.

The output signals generated by the light measurement sensorare transmitted to one or more processor(s)for evaluation as a function of one or more hardware or software modules. As used herein, the term “module” refers, generally, to one or more discrete components that contribute to the effectiveness of the presently described systems, methods and approaches. Modules can include software elements, including but not limited to functions, algorithms, classes and the like. In one arrangement, the software modules are stored as software in memoryof processor, as shown in.

Modules can, in some implementations, include discrete or specific hardware elements. In one implementation, processoris located within the same device or enclosure as the light measurement sensor. For example, bot the processorand the light measurement sensorare components of a spectrophotometer. However, in another implementation, processoris remote or separate from the light measurement sensorand communicates over one or more communication linkages.

In one configuration, processoris configured through one or more software modules to generate, calculate, process, output or otherwise manipulate the output signals generated by the light measurement sensor.

In one implementation, processoris a commercially available computing device. For example, processormay be a collection of computers, servers, processors, cloud-based computing elements, micro-computing elements, computer-on-chip(s), home entertainment consoles, media players, set-top boxes, prototyping devices or “hobby” computing elements.

Furthermore, processorcan comprise a single processor, multiple discrete processors, a multi-core processor, or other type of processor(s) known to those of skill in the art, depending on the particular embodiment. In a particular example, processorexecutes software code on the hardware of a custom or commercially available cellphone, smartphone, notebook, workstation or desktop computer configured to receive data or measurements captured by one or more light measurement sensorseither directly, or through a communication linkage.

Processoris configured to execute a commercially available or custom operating system, e.g., Microsoft WINDOWS, Apple OSX, UNIX or Linux based operating system in order to carry out instructions or code. In a particular implementation, processoris a computer, workstation, thin client or portable computing device such as an Apple iPad/iPhone® or Android® device or other commercially available mobile electronic device configured to receive and output data to or from databaseand the light measurement sensor.

In one or more implementations, processoris further configured to access various peripheral devices and network interfaces. For instance, processoris configured to communicate over the internet with one or more remote servers, computers, peripherals or other hardware using standard or custom communication protocols and settings (e.g., TCP/IP, etc.).

Processormay include one or more memory storage devices (memories). The memory is a persistent or non-persistent storage device (such as an IC memory element) that is operative to store the operating system in addition to one or more software modules. In accordance with one or more embodiments, the memory comprises one or more volatile and non-volatile memories, such as Read Only Memory (“ROM”), Random Access Memory (“RAM”), Electrically Erasable Programmable Read-Only Memory (“EEPROM”), Phase Change Memory (“PCM”), Single In-line Memory (“SIMM”), Dual In-line Memory (“DIMM”) or other memory types. Such memories can be fixed or removable, as is known to those of ordinary skill in the art, such as through the use of removable media cards or modules. In one or more embodiments, the memory of processorprovides for the storage of application program and data files. One or more memories provide program code that processorreads and executes upon receipt of a start, or initiation signal.

The computer memories may also comprise secondary computer memory, such as magnetic or optical disk drives or flash memory, that provide long term storage of data in a manner similar to a persistent memory device. In one or more embodiments, the memory of processorprovides for storage of an application program and data files when needed.

As shown in, processoris configured to store data either locally in one or more memory devices. Alternatively, processoris configured to store data, such as measurement data or processing results, in a local or remotely accessible database. The physical structure of databasemay be embodied as solid-state memory (e.g., ROM), hard disk drive systems, RAID, disk arrays, storage area networks (“SAN”), network attached storage (“NAS”) and/or any other suitable system for storing computer data. In addition, databasemay comprise caches, including database caches and/or web caches. Programmatically, databasemay comprise flat-file data store, a relational database, an object-oriented database, a hybrid relational-object database, a key-value data store such as HADOOP or MONGODB, in addition to other systems for the structure and retrieval of data that are well known to those of skill in the art. Databaseincludes the necessary hardware and software to enable processorto retrieve and store data within database.

In one implementation, each element provided inis configured to communicate with one another through one or more direct connections, such as though a common bus. For example, when each of the components are contained within the same form-factor (such as a spectrophotometer), each component is connected to the processor, and optionally one another, through one or more direct electrical linkages. Alternatively, each element is configured to communicate with the others through network connections or interfaces, such as a local area network LAN or data cable connection. In an alternative implementation, the light measurement sensor, processor, and databaseare each connected to a network, such as the internet, and are configured to communicate and exchange data using commonly known and understood communication protocols.

In one arrangement, processorcommunicates with a local or remote display deviceto transmit, displaying or exchange data. In one arrangement, the display deviceand processorare incorporated into a single form factor, such as a spectrometer, that includes an integrated display device. In an alternative configuration, the display deviceis a remote computing platform such as a smartphone or computer that is configured with software to receive data generated and accessed by processor. For example, processoris configured to send and receive data and instructions from a processor(s) of a remote display device.

This remote display deviceincludes one or more display devices configured to display data obtained from processor. Furthermore, display deviceis also configured to send instructions to processor. For example, where processorand the display device are wirelessly linked using a wireless protocol, instructions can be entered into display devicethat are executed by the processor. Display deviceincludes one or more associated input devices and/or hardware (not shown) that allow a user to access information, and to send commands and/or instructions to processor. In one or more implementations, the display devicecan include a screen, monitor, display, LED, LCD or OLED panel, augmented or virtual reality interface or an electronic ink-based display device.

It will be understood and appreciated that the components described here can be used to measure the light properties of a sample. In one or more implementations, samplecan be any type or form of physical article having color or spectral properties in need of analysis. For ease of reference and discussion, the foregoing descriptions the samplerefers to an article or material that has stable and uniform color and can be evaluated by currently available spectrophotometers.

In one or more further or alternative implementations, sampleis a calibration article. Here, the calibration article has specific properties making it suitable for stable measurements over time. For instance, sampleis a ceramic calibration tile. In one or more further implementations, sampleis a white ceramic calibration tile. However, in alternative configurations, sampleis a black calibration tile.

Those possessing an ordinary level of skill in the requisite art will appreciate that additional features, such as power supplies, power sources, power management circuitry, control interfaces, relays, adaptors, and/or other elements used to supply power and interconnect electronic components and control activations are appreciated and understood to be incorporated.

With particular reference to, a process and method for calculating the second-order diffraction error in a measurement and correcting for such error is provided.

It will be appreciated that when the narrow-band light from a source (such as a narrow-band illuminator) reaches the grating-based spectro-sensor in the spectrophotometer, either directly or indirectly, it will generate a signal on the sensors as a function of wavelength, and both the base signal (first order) and the second-order diffraction signal will be captured, as shown in.

In order to compensate for the second-order diffraction, it is first necessary to define a range of wavelengths where the SODE arises. As shown in, a processor (such as processor) is configured by one or more modules to select or determine a start wavelength λLand end wavelength λLand all the intermediate wavelengths that will be compensated, as shown in step. It will be appreciated that the wavelength range λL-λL, (where L stands for long) is within the effective wavelength range of the measurement sensor. For example, the wavelength range λL-λLis encompassed by the wavelength range that can be evaluated by a light measurement sensor of a particular make and model of spectrophotometer.

As shown in, in one arrangement, the processoris configured by a wavelength determining moduleto select a wavelength that is within the range of the measurement apparatus. In one arrangement, the wavelength determining moduleconfigures the processorto automatically select a wavelength range for L-L. Alternatively, the wavelength determining moduleconfigures the processorto receive user input that allows selection of a desired, calculated or custom L-Lrange. In either case, the wavelength range for L-Lcorresponds to the portion of the entire wavelength range of the spectral sensor where second order diffraction errors occur.

Next, one or more processors (such as processor) is configured by the wavelength determining moduleto select a short wavelength range as shown in step. Here, the wavelength determining moduleconfigures the processorto automatically select a wavelength range for S-S(where S stands for short). In one particular implementation the corresponding base wavelength λS=λL/2 and λS=λL/2, and all the intermediate short wavelengths are half values of the long wavelengths between λLand λL. It will be appreciated that the wavelength range λS˜λSis within the effective wavelength range of the measurement sensor.

In one or more further implementations, where the wavelengths of pixels in the short wavelength range (S-S) do not directly match that of the long wavelength range (L-L), for example, because the long wavelength divided by 2 falls between the wavelength of two adjacent pixels, the wavelength determining moduleconfigures the processorto perform an interpolation process to generate the proper wavelength match.